import matplotlib.pyplot as plt
import numpy as np

from shiny import reactive, render
from shiny.express import input, ui

ui.input_slider("n", "Number of observations", min=0, max=1000, value=500)
ui.input_action_button("go", "Go!", class_="btn-success")


@render.plot(alt="A histogram")
# Use reactive.event() to invalidate the plot only when the button is pressed
# (not when the slider is changed)
@reactive.event(input.go, ignore_none=False)
def plot():
    np.random.seed(19680801)
    x = 100 + 15 * np.random.randn(input.n())
    fig, ax = plt.subplots()
    ax.hist(x, bins=30, density=True)
    return fig
